The present invention relates to deflection yokes used to adjust electron beam deflection in cathode ray tubes. In particular, the present invention pertains to conductive plates which may be used to replace or augment the deflection yokes used in cathode ray tubes.
The invention relates to cathode ray tube (CRT) apparatuses having a display screen, an electron gun system to generate at least one electron beam, and a deflection unit (or deflection yoke) for deflecting the electron beam(s) in accord with a changing pattern.
In monochrome CRT""s the electron gun system generates one electron beam which is directed onto the display screen, whereas color display tubes use electron gun systems which generate three electron beams which converge on the display screen.
Referring to FIG. 1 which depicts a conventional cathode ray tube (CRT) apparatus including a vacuum envelope 10 which commonly resembles a trumpet shaped vacuum envelope having a narrow neck portion 12 and a wider portion which includes a display screen 14. Toward one end of the narrow neck portion 12 lies the electron gun system 16. At the opposite wider end of the envelope lies the display screen 14 which includes phosphorescent materials which radiate light when struck by electrons emitted from the electron gun system 16.
The deflection yoke 20, (also, referred to as a deflection system or deflection unit) commonly positioned about the narrow neck portion of the envelope, is designed to deflect the electron beam(s) emanating from the electron gun system 16. The deflection yoke 20 is used to deflect the electron beam from its normal undeflected straight path, so that the beam impinges upon selected points on the display screen 14 to provide visual presentations. By varying the magnetic (or deflection) fields created by the deflection yoke 20 in a suitable manner, the electron beam(s) can be deflected upwards or downwards and to the left or to the right over the display screen. By simultaneously modulating the intensity of the beam a visual presentation of information or a picture can be formed on the display screen. A common example is the display of video images.
In three beam electron gun systems 16 the three deflected beams which correspond to different colors (for example, red, green, and blue (RGB)) are deflected such that the three beams each converge at the display screen 14 to produce the appropriate color in a manner known to those having ordinary skill in the art.
The shape and intensity of the magnetic deflection fields created by a deflection yoke vary throughout the CRT and along a distance the electron beam must travel. One typical field pattern is known as a xe2x80x9cbarrelxe2x80x9d field, an example of which is shown in FIG. 2 as a cross-section perpendicular to the CRT axis. As is well known in the art the field is called a xe2x80x9cbarrelxe2x80x9d field because the separation between field lines 5 is greater near the center regions of the deflection field. The field depicted in FIG. 2 results in a so-called North/South (NS) distortion xe2x80x9cpin-cushion of otherwise horizontal lines. Another common field pattern is the so-called xe2x80x9cpin-cushionxe2x80x9d field depicted in FIG. 3. As is also well known, the field is called a xe2x80x9cpin-cushionxe2x80x9d field because the separation between field lines 5 decreases near the center regions of the deflection field. The field depicted in FIG. 3 results in a so-called NS barrel distortion. These and other field variations are known and used by practitioners having ordinary skill in the art in the design and application of suitable deflection yoke""s 20.
Many different coil configurations are used to establish the desired deflection field at each location within the vacuum envelope 10. Typical examples of coils known in the art are saddle coils (FIG. 4a), which are used in opposing pairs, and toroidal coils (FIG. 4b).
A common type of deflection yoke comprises two sets of deflection coils positioned about the display enabling deflection of the electron beam in two directions which are transverse to each other. By way of example, a first set of saddle coils uses two coils which are arranged on oppositely located sides of the neck portion of the vacuum envelope. Another set of saddle coils can be oriented relative to the first set of coils by orienting them at 90xc2x0 about the neck portion of the vacuum envelope. Such an arrangement is commonly referred to as a saddle-saddle (or S-S) coil arrangement (after the xe2x80x9csaddlexe2x80x9d shape of the deflection coils). One set of coils (the vertical deflection coils), when energized deflects the electron beam in a first (vertical) direction. Another set of coils (the horizontal deflection coils), when energized deflects the electron beam in a direction transverse to the first direction. The sets of deflection coils upon energization, generate a dynamic magnetic multi-pole field comprising at least a dipole component and a multi-pole component. Alternatively, the vertical set of saddle coils may be replaced with a so-called toroidal coil to form a hybrid coil arrangement called a saddle-toroidal (or S-T) arrangement. Still other applications may not use saddle type coils at all, instead using pairs of toroidal coils (in a toroidal-toroidal (T-T) arrangement).
Using a saddle-saddle arrangement as an example, the two sets of deflection coils are energized to produce two substantially orthogonal deflection fields. Inside the vacuum envelope the fields are substantially perpendicular to the path of the undeflected electron beam(s). A cylindrical core, comprised of material having a very high relative permeability (e.g., on the order of 1000), positioned to closely engage the sets of deflection coils (in a saddle-saddle configuration) is used to concentrate deflection fields generated by the coils and to increase the flux density in a deflection area. Also, an insulating liner is positioned between the two sets of coils to prevent electrical shorting between the coils.
With continued reference to FIG. 1, a cross section view of a saddle-toroidal (S-T) configuration is shown. A vacuum envelope 10 including a neck portion 12, an electron gun system 16 for producing at least one electron beam, and a display screen 14 are shown. Also shown is a S-T type deflection yoke 20 including a pair of saddle deflection coils 21a and 21b positioned about the neck 12 of the envelope 10. The deflection yoke 20 also includes an electrical insulation layer 25 positioned between the saddle coils 21a, 21b and a toroidal coil 23. The toroidal coil 23 is commonly wrapped around a ferrite core 24.
In order to satisfy certain requirements regarding picture quality, the (dynamic) magnetic deflection fields are often strongly modulated. For example, as is known in the art, the stringent convergence requirements in three inline color television systems necessitate, different polarities and different magnitudes of magnetic multi-pole components along the axis of the yoke from gun side to screen side. xe2x80x9cLinexe2x80x9d field is synonymous with horizontal field because this field results in forming lines by pushing electrons from left to right on screen. xe2x80x9cFieldxe2x80x9d is same as xe2x80x9cverticalxe2x80x9d because vertical deflection refreshes the whole field (i.e., whole screen) after all horizontal lines are scanned. Further, in systems where the electron beam(s) must negotiate a large deflection angle (such as in wide screen applications), it is particularly difficult to achieve the required deflection field modulations using only the two sets of deflection coils. In some cases this can only be achieved at very high cost, in other cases the required field modulation is simply not possible to achieve using two sets of coils.
Many approaches have been tried to solve the complex problem of adjusting the deflection field to achieve the desired field modulation at each point in the CRT. One approach has been to include a variety of xe2x80x9chelpersxe2x80x9d which modify the deflection field in ways which are not possible with present art deflection coils alone within the given time frame or cost constraints. Typical helpers are small permanent magnets, (e.g., U.S. Pat. No. 4,396,897) small or large pieces of permeable material placed in specific locations, or the use of auxiliary coils.
What is needed is a low cost, easily manufacturable, highly sensitive method and apparatus for modulating the deflection field in a CRT. Also needed is a replacement for the many xe2x80x9chelpersxe2x80x9d currently used to modulate the deflection field. What is also needed is an easily manufacturable low cost replacement for the conventional coil systems currently used to control the deflection field in a CRT.
In one embodiment the present invention can be characterized as a system that displays video images comprising a cathode ray tube means including an electron gun system for producing at least one electron beam, which in response to a magnetic field converges onto a display screen causing video images corresponding to the at least one electron beam to be displayed thereon; and a deflection yoke means for producing the magnetic field, the deflection yoke means comprising a plurality of electrical coils arranged such that when said plurality of coils are energized a line or horizontal deflection field is formed and a field or vertical deflection field is formed transverse to said line deflection field, the deflection yoke further including at least one conducting plate which includes therein one or more magnetic field shaping features such that when the at least one conducting plate is electrically energized, the magnetic field is enhanced and balanced to compensate for at least one of undesired barrel distortion, pin-cushion distortion, and misconvergence errors. The inventors further contemplate embodiments where in the electron gun system produces a plurality of electron beams, including electron gun systems which produce three electron beams, each corresponding to a respective color wherein, in response to the magnetic field, the electron beams converge onto the display screen producing color video images corresponding to the converged electron beams.
The invention further contemplates conducting plate embodiments which include magnetic field shaping features. In one conducting plate embodiment the field shaping features include a slit extending along a length of the conducting plate. A further embodiment includes a conducting plate having a length, a rear end, and a front end wherein the field shaping features include having at least one slot in the conducting plate, the at least one slot being oriented transverse to the length of the conducting plate. Or alternatively, the field shaping features may include having two slots, a first slot positioned near the rear end of the conducting plate and a second slot positioned near the front end of the conducting plate and wherein the first slot and the second slot are each oriented transverse to the length of the conducting plate. A further embodiment includes a conducting plate having a plurality of apertures formed therein. Another embodiment includes a conducting plate wherein the field shaping features included having apertures in the conducting plate including a slot extending a distance along a length of the conducting plate. In another embodiment the conducting plate has a length, a rear end, and a front end, and wherein the conducting plate includes an opening having an increasing angular width from the front end to the rear end.
Another embodiment includes a vacuum envelope having a neck portion and a display screen and having a electron gun system for producing at least one electron beam wherein, in response to a magnetic field, the at least one electron beam converges onto the display screen causing video images corresponding to at least one electron beam to be displayed thereon and also including a deflection yoke for producing the magnetic field. The deflection yoke comprises at least one conducting plate which when electrically energized forms the magnetic field.
In a further embodiment an apparatus for displaying video images comprises a vacuum envelope including a neck portion and a display screen an electron gun system for producing a plurality of electron beams each corresponding to a respective color and, in response to a magnetic field, for converging the electron beams onto the display screen causing video images corresponding to the converged electron beams to be displayed thereon. This embodiment includes a deflection yoke comprising a plurality of conducting plates including magnetic field shaping features, the conducting plates when electrically energized form the magnetic field which converges the electron beams onto the display screen.
Other features of the present invention are disclosed or made apparent in the section entitled xe2x80x9cDETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS.